


A Natural Curiosity

by orphan_account



Category: Undertale
Genre: 1-S/2-P, Fontcest, Growing Up is Hard, Handplates, M/M, Masturbation, Soul Sex, Trauma, the importance of sex ed
Language: English
Status: Completed
Published: 2020-03-17
Updated: 2020-03-17
Packaged: 2021-02-28 21:00:28
Rating: Mature
Warnings: Underage
Chapters: 1
Words: 3,214
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/23163643
Author URL: https://archiveofourown.org/users/orphan_account/pseuds/orphan_account
Summary: 1-S and 2-P were told not to touch each others souls. But they were never told not to touch their own.
Relationships: Papyrus/Sans (Undertale)
Kudos: 53





	A Natural Curiosity

**Author's Note:**

> Occurs at some point between the 'blue magic lesson' and when Gaster's face cracks.

Maybe it shouldn't be so surprising. After all, Gaster kept them in a tiny cell with very little to occupy them except interaction with each other. No toys or games, save a color cube and a 'dust bunny' they had constructed out of the stuffing of their single pillow. Gaster spent only a portion of his waking hours with them, and there was not much around to stimulate the minds of a pair of young monsters, left alone for most of the day in a very, very small room.

Another thing to keep in mind was that the two brothers were growing fast. Though they were both only a few years old, their bodies had matured to adolescence. This was intentional, as Gaster didn't like to think of them as children, and endeavored to make them un-childlike as quickly as possible.

The third factor, it must be admitted, was their necessarily limited understanding of the outside world, of its ways and mores and taboos. Gaster never bothered to explain to them how different monsters reproduced, for example. They didn't even know of reproduction as a concept, considering that Gaster had made them in tubes from pieces sliced off his own body and soul. It was irrelevant. Unnecessary distractions. So, the topic was ignored in their already highly constrained education.

They were told, of course, not to run around naked, because it was inappropriate. And they were told not to touch the soul of another monster, because it was rude.

That was the start of it. They were told not to touch each others souls. But they were never told not to touch their own.

It was curiosity, when they were young. They both agreed that it felt 'weird' to touch one's own soul, but also somewhat relaxing. It felt nice, to hold it while falling asleep. It kind of tingled.

They spoke of their experiences freely. They had never been told to be ashamed, and they had no one else in their lives to shame them, no one but each other and Gaster.

Subject 2 woke in the middle of lights-out, rising up from a dream of clutching hands and a cool, shivery light. He rubbed his eyesockets, glanced at his brother, who was still asleep, and sighed. He had no way of telling what time it was, but he didn't feel sleepy anymore. And with his brother lying sprawled across his legs, he couldn't exactly move.

So, he did what he often did when bored and left to his own devices in the middle of the night. He hitched his hospital gown up, reached his arm down and under his ribcage, then up and in to palm his soul. It was an awkward position, but the only one in which he could access his soul at all, protected by his ribs as it was. He closed his eyes and breathed deeply, squeezing his heart gently and rhythmically, sometimes rubbing his thumb in small circles over the top. It was warm, with the texture of hard rubber, and glowed faintly between his fingers at the stimulation.

It felt nice. Really nice. Subject 2 sighed and tilted his head back against the wall, brother still snoring away at his feet. He continued in that vein for a while, then began to notice something different, that he hadn't noticed before. His soul was... softening? It was feeling more... pliant, like he could press his fingertips into it and leave a mark, if he wanted to. And as it did, it also seemed to be getting more sensitive, tingling more intently, almost aching.

He paused mid-motion, puzzled. Was this normal? Was something wrong with him? It wasn't painful, but it... well, okay, it actually felt good. Like he never wanted to let go. So... it couldn't be bad, right? Maybe he should wake up his brother and ask him if he knew what-

Subject 2 let go of his soul for a moment, and it throbbed powerfully, almost painfully, in response. His fingers were quick to close around it again. He didn't want to stop. He could ask his brother about it later.

He gave his softened soul a gentle squeeze, and a shiver went through his body, rattling his vertebrae. That was so... so _good_.

His hands were inexpert, his angle uncomfortable, but the increasing tremors as he squeezed his soul were intoxicating. He was warm all over and he wanted more, he wanted...

He wasn't sure what he wanted.

The young skeleton panted, eyes screwed shut. God, what was this? What was happening to him? He felt moisture, and glanced down, through his ribs, to see the cause. He gasped.

His soul was sweating, no, it was _melting_ , was dripping, running like soft wax over his fingers. He wondered, with a jolt of fear, if he was dying. It didn't hurt, but it was so intense, so strange, his soul was so soft, he- he could push his finger right through the middle-

And when 2-P pushed his finger in, burying it two knuckles deep in his own soul, he couldn't hold back a cry.

That's when Subject 1 woke up, sprawled across his brother's legs, and heard the shout of - he could only imagine - pain. He bolted upright and looked at Subject 2 just as his brother's soul liquefied completely, taking on the consistency of honey and dripping down from his hand, running down his arm.

"OH, _OH_ ," said Subject 2, climax sparking through him, and his hand fell limply, exhaustedly, out of his ribcage.

Subject 2's eyes were flickering deep magenta, a color 1-S had never seen them go before, and the expression on his face defied his brother's ability to describe. Terrified, Subject 1 let out a gasp of distress. "bro! bro!! are you- your soul! oh god...!"

"S-SORRY," his brother muttered, sounding utterly spent in the wake of his first ever orgasm. "OH BOY. WOWIE. I DIDN'T MEAN TO WAKE YOU."

"what? what happened, why-" Subject 1 peeked into 2's ribcage, and to his surprise, his brother's soul was... coalescing? It still looked liquid, but it was coming back together a bit, floating back to its proper place behind the ribs. It was looking more soul-shaped by the second. "what were you-?"

"I'M NOT SURE," Subject 2 answered truthfully. After all, he'd never been taught. He smiled at his brother and glowed his eyes reassuringly. "I'M OKAY, THOUGH. THAT WAS REALLY... PHEW. STRANGE."

Subject 1 blinked in confusion. "your soul just melted!"

"IT DID? OH. WELL, IT LOOKS BETTER NOW."

Eventually, Subject 2 managed to calm his brother, reassuring him that he was fine, really, more than fine, he felt great!

2-P didn't have trouble falling back to sleep, but 1-S was still awake. He stayed up for a while longer, watching his brother snore softly, to make sure nothing else happened to his soul. Eventually, sleep caught up to him as well.

* * *

"YOU SHOULD TRY IT, BROTHER!"

"what, melting my soul?"

"YES! IT REALLY DOES FEEL NICE."

Subject 2 still wasn't sure what it was, exactly, that made it feel so good when his soul melted. He was starting to think he should ask the doctor, but his brother had mentioned that the doctor might tell him to stop, which made him hesitate to reveal it.

And it was... starting to become a habit. The soul melting. He generally would do it during lights-out, to make sure the doctor never interrupted. It was nice, a relief from the stresses of the day, and he always slept sounder afterwards, with fewer nightmares.

1-S knelt on the floor, looking uncertain. "...you sure it'll come back together?"

"IT ALWAYS DOES WITH ME!"

"yeah but you're..." 1-S twiddled his fingers, phalanges clacking. "stronger. your soul is bigger."

2-P frowned. "WHY WOULD THAT MAKE A DIFFERENCE?"

"i dunno. it does with everything else."

"PLEASE, BROTHER? I WANT YOU TO KNOW WHAT IT'S LIKE."

Subject 1 snorted and rolled his eyes, but hitched up his gown regardless. "if my soul falls out of my body and won't go back, it'll be your fault." His fingers closed around his soul. "so, am i supposed to do anything special?"

"JUST RUB IT. AND KEEP GOING." 2-P's eyes glowed orange with curiosity. This would be interesting, to see it from the outside.

Subject 1 hadn't been at it for long before his face screwed up and his breaths started coming in heavy. His toes curled and he leaned forward, trying to get a better grip. And even though it was closed, Subject 2 could see his brother's good eye glowing magenta.

He couldn't really see what was happening to 1-S's soul from where he sat, but when his brother gasped and shook he could guess that his soul had melted. The pink under his eyelid flickered brighter for a moment, then dimmed.

"hhhhah, oh, nh." 1-S flopped onto his back, extracting his arm from under his ribcage. "oh my god."

2-P looked smug. "WHAT DID I TELL YOU?"

"wow." Subject 1 managed to lift his head long enough to glance down at his soul. "huh, it's coming back together."

"SEE? YOU HAD NOTHING TO WORRY ABOUT."

"ehh, you didn't know that." Still, the smile on 1-S's face was genuine.

* * *

"MMMPH." Subject 2 wiggled from side to side uncomfortably. Both his arms were in stiff casts from the doctor's latest procedure, but even if he could bend them, the sharp shooting pain would quickly bring an end to his efforts.

"that's the best i can do," said 1-S softly, his green magic fading. "what did he even to do to you? are these metal pins?"

"I THINK SO? I DIDN'T GET A GOOD LOOK AT, UM, WHAT HE WAS DOING."

Subject 1's eyes went dark. "and he never explains. i shouldn't be surprised."

"IT'S ALRIGHT, I'LL... BE OKAY, ONCE WE GET OUR RATIONS. I'M SURE." Subject 2 tried to smile reassuringly. "WE SHOULD TRY TO SLEEP UNTIL THEN."

Subject 1 stood up. "you'll need the whole bench, for your arms. I'll sleep on the floor."

A few minutes later, as Subject 2 lay on the bench, he could hear the telltale soft groans as his brother melted his soul nearby. They both did it almost nightly now, and sometimes twice if they got a break during the day.

Subject 2 rolled onto his side and winced at the pressure on his arm, so rolled back onto his back. He was very uncomfortable in the casts, and knew it would be difficult to get to sleep. It didn't help that he couldn't even reach his own soul to melt it, not from this position.

1-S let out a stuttering gasp as he finished, and 2-P grunted in frustration as his soul throbbed for want of attention. For a moment, there was silence.

"bro?"

"MMRPH?"

"your- are your arms still hurtin?"

2-P sighed. "ONLY WHEN I ROLL ON MY SIDE. IT'S MOSTLY JUST UNCOMFORTABLE, AND I CAN'T EVEN MELT MY SOUL LIKE THIS."

"oh." Another pause. Then, "maybe i can do it for you, tonight?"

"WE'RE NOT SUPPOSED TO TOUCH EACH OTHERS' SOULS." The answer was immediate, automatic, ingrained since what had passed for their childhood.

"why, cause he says so? why do we gotta listen to everything he says?"

Subject 2's voice was raspy, breathless at the thought of rebellion. "WE'LL BE PUNISHED."

"how's he gonna know?" In the darkness, Subject 1's voice was coming from right next to his brother's ear. "i'm not gonna tell."

"I- IF YOU'RE SURE. BE CAREFUL, I- OH!" 2-P felt his brother lift the fabric of his gown and sneak a hand over his ribcage. "CAREFUL..."

"wait, hold on, it'll be easier if I go from beneath."

The brothers were very familiar with each other, but Subject 2 couldn't remember Subject 1 ever touching the _insides_ of his ribs. It was a part of his body that he hardly paid attention to, and feeling someone else's hand groping around in there was very strange.

"wait, okay, here we go." Subject 1's fingers brushed his brother's soul, and Subject 2 shivered, partly with nerves and partly from the sensation.

"BROTHER..."

"it's okay. it's just me. it'll make you feel better, right?" 1-S glowed his eye from a spot next to 2-P's ribcage, and 2-P glowed back. "i'd never hurt you."

2-P shifted position slightly, the arm casts digging into his shoulders. "I KNOW."

Then his brother's hand closed over his soul, rubbing the lobes in gentle circles. 2-P let out a soft whimper. "CAN YOU... DO THAT FASTER, PLEASE? I USUALLY DO IT FASTER."

1-S nodded, and the larger brother groaned and arched his spine as his soul began to throb. It was even more intense, somehow, than it usually was.

"huh," said 1-S after a moment. "i didn't know you could move it." As he said this, he stopped rubbing, and Subject 2 made an unhappy noise.

"W-WHAT, MNH, DO YOU MEAN?" he panted.

"i mean, i can move your soul. i can move it around in your ribcage." To illustrate, 1-S grabbed his brother's soul and moved it around in circles, like it was a toy.

Subject 2 grunted in frustration. "OH, WELL, CAN YOU KEEP GOING? I'M, IT'S ALMOST MELTED, IT'S _ALMOST_ THERE I CAN FEEL IT..."

"yeah, sure. heh, sorry." 1-S smiled and resumed rubbing, pushing his fingertips into the soft soul. "how's that?"

"GOOD. KEEP GOING, DON'T STOP. PLEASE DON'T STOP, IT'S _SO GOOD._ " 2-P's joints rattled and he moaned, loud, when his soul finally collapsed into liquid.

Looking smug, Subject 1 withdrew his arm from under his brother's gown, then blinked in puzzlement as he saw bits of melted soul still sticking to his hand. "uh."

"THANK YOU, BROTHER," sighed Subject 2. "WOWIE. THAT WAS A GOOD ONE."

"bro?"

"GOODNIGHT."

"bro, your soul gunk is still stuck to my hand."

"HMM?" Subject 2 lifted his head slightly. "WHAT DO YOU MEAN? IT ALWAYS COMES BACK TOGETHER."

"well it's not. are- do you feel okay?"

"I FEEL FINE." 2-P could see some kind of shimmering substance on his brother's fingers. "OH, UH, MAYBE WE CAN PUT IT BACK?"

1-S nodded and reached back into 2-P's ribcage, where his soul had almost finished coalescing into its normal shape. He shook his hand, but it didn't come off to rejoin the rest, so he tried rubbing his fingers against the still-puttylike soul. Subject 2 _yelped._

Subject 1 startled. "what!? oh god, are you okay?"

"NGH, OH, IT DOESN'T FEEL GOOD TO TOUCH IT AGAIN AFTER IT MELTED." 2-P grimaced. "IT'S KIND OF TENDER."

"oh, gosh, sorry." 1-S swiftly withdrew his hand.

"IT'S ALRIGHT, I KNOW YOU DIDN'T MEAN IT."

1-S glanced at his hand. "... your soul stuff is still on me."

"UM..."

"i'll just wipe it off i guess? i'll put it on you, so it can reattach." Subject 1 wiped his hand on the inside of Subject 2's gown, and finally the soul gunk came off.

But it didn't reattach. And unfortunately, the next day was a wash day.

* * *

Dr. Gaster fast-forwarded through the recording of the subject's cell. Talking, playing with the color cube, practicing magic, talking, masturbating, talking some more... all their usual activities. He knew what they had been up to, and he didn't have a _problem_ with it, so to speak. It was vaguely interesting, from an anatomical standpoint, that they were capable of self-stimulation, but not really noteworthy. Most monsters with accessible souls could do so, and the subjects were formed off of a monster's template.

 ~~And if Dr. Gaster tended to avert his gaze when he saw them touch themselves, it certainly wasn't due to any sense of embarrassment or impropriety. That would suggest that the subjects were~~ ~~ _people,_~~ ~~beings deserving of modesty and propriety~~ ~~ _._~~ It just... wasn't scientifically noteworthy. Their bodies and souls were developing, so they explored their bodies and souls. Natural curiosity. That was all.

But this... Dr. Gaster glanced down at the essence-stained surgical shift. Every week, he would drop off clean green shifts and take the old ones for a wash. It was a normal procedure, one the subjects were well-accustomed to.

He certainly hadn't expected to find the stains on Subject 2's shift. Nor, when he analyzed them, had he expected it to be soul essence. This was troublesome. It suggested that the subjects' explorations had crossed a line.

The only question was, what kind of consequence was suitable? He'd have to be careful, and time his intervention correctly. Gaster wasn't sure if the subjects were capable of making a biological child, but he'd have to nip this behavior in the bud before it went any further. It may only be a matter of time before they tried touching their souls together directly, and that would be a terrible mistake for everyone involved.

* * *

It was not hard to catch them in the act. Their one go, apparently, had emboldened the subjects, and it only took one night of viewing them on the live camera feed before he saw 1-S up to his elbows in 2-P's ribcage. Gaster froze, a cold feeling in his chest. ~~It wasn't that they were nominally brothers, that bothered him.~~ Things can't be brothers. ~~It especially wasn't because it reminded him of how, in all his years, he had never felt such a touch from another monster.~~ It was dangerous behavior, and needed to be stopped.

Dr. Gaster walked briskly to the subject's cell, leaving the lights off in the dark hall as he approached. He could hear 2-P moaning loudly, shamelessly, not even bothering to muffle himself, ~~like any other monster of his age might, not wanting to be caught by their parents~~.

The subjects were too absorbed in their activities to hear Gaster's footsteps, and so when the doctor arrived at the cell, they were still at it. 2-P was still squirming and kicking in pleasure, eyes glowing magenta, and 1-S was still vigorously massaging his soul, when they both turned blue.

* * *

Some indeterminate amount of time later, a young skeleton lay in a twin bed, looking over at his brother, who was laying quietly and staring back from an identical one. They did not know anything. Not their names, not where they were, not the identity of the huge furred monster who had brought them here and given them clothes.

Still, it felt... wrong. This isn't how they should sleep. One crawled out of the covers, and, seeing the movement, his brother did too. They met each other in the middle of the floor, and, by sudden impulse, one reached under his brother's ill-fitted shirt, into his rib cage, because this is what you do before sleep, right...?

No. His brother froze, and so did he. They sat there, knee-to-knee, for several long, dark, silent seconds. There was no memory that came with it, no phantom sensation of pain, just dread, and a feeling... that you should _never, ever, touch someone else's soul_.

"Don't," his brother whispered, frightened of a shadow neither of them could see, and he obliged, removing his hand, trembling and feeling his brother trembling, too. They enveloped each other in an embrace, forgiving and being forgiven.

Asgore found them that way in the morning, sleeping in each other's arms.


End file.
